How do I add a background image to the header? I bought this plugin
WoltLab Cloud
File
Header Image Changer (Banner Rotation) for WoltLab Suite

You want to have diversion on your website? Than you can create it now with the Header Image Changer in a very easy way! It does not matter if you want to dynamically change your header background image or your logo, both is supported.
but I don't need the image to change all the time, and this plugin reloads my one image with each page. BTW it's also supposed to change the logo but this feature doesn't work.